EPA Releases Draft Dioxin Report

July 6th, 2010

In May 2010 the Environmental Protection Agency (EPA) released a response to key comments and recommendations made by the National Academy of Sciences (NAS) on the EPA’s 2003 draft dioxin reassessment. This response addresses the human health and exposure risk assessment of dioxins.

The EPA’s draft report includes significant new analyses that relate to issues raised by the NAS, including potential cancer and non-cancer human health effects that may result from exposures to dioxins. The NAS identified three areas that require substantial improvement:

justification of approaches to dose-response modeling for cancer and non-cancer endpoints;

transparency and clarity in the selection of key data sets for analysis; and

Thus, the new draft dioxin report includes an oral reference dose (RfD) for 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) – considered by the EPA to be among the most toxic of the dioxin-like compounds, and the most studied of these compounds.

The draft report will undergo external peer review by an expert panel of scientists convened by the EPA’s Science Advisory Board. The EPA plans to use the feedback and recommendations of this expert panel, as well as public comments, to complete its draft dioxin reassessment.

Dioxin is a general term referring to a group of chemical compounds that share certain chemical structures and biological characteristics. Several hundred of these compounds exist and are members of two dioxin families, polychlorinated dibenzo dioxins (PCDDs) and polychlorinated dibenzo furans (PCDFs), as well as 12 “dioxin-like” compounds, more commonly referred to as polychlorinated biphenyls (PCBs). Sometimes the term dioxin is also used to refer to TCDD. Dioxins are highly persistent in the environment and are formed during combustion or burning. Sources of dioxins include commercial or municipal waste incineration, the burning of fuels such as wood, coal, or oil, and natural phenomena such as forest fires. Dioxins are slow to decompose in the environment and can be deposited on plants and absorbed by animals and aquatic organisms. While dioxin levels in the United States environment have been declining for the last 30 years due to reductions in emissions from artificial sources, the chemicals break down so slowly that dioxins from past releases will persist in the environment for many years to come.

More information on the report is available at http://www.epa.gov/dioxin/

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The document that is the subject of this article lists in Volume 1 – Sources of Dioxin-Like Compounds in the United States. It does not specifically mention polyfluorinated and polybrominated dioxins, furans and biphenyls. Information about all the assessments the EPA is currently working on is on the EPA Risk Assessment Portal at http://www.epa.gov/risk/. You may also find information about these compounds from the following websites: the CDC’s website,the International Programme on Chemical Safety and the World Health Organization.